Power bank



FIG. 1 is a perspective view of a power bank showing my new design;

FIG. 2 is a front side view thereof;

FIG. 3 is a back side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines in the drawings are for the purpose of illustrating portions of the power bank that form no part of the claimed design. 

CLAIM The ornamental design for a power bank, as shown and described. 